Many inorganic and almost all organic chemicals have IR spectra that can be used for identification, characterization and determination of their concentration in mixtures and it has already been proposed to use for the purpose probes of the kind specified.
In its simplest form an IR fiber optic probe for spectral analysis consists of two optical fibers capable of transmitting IR radiation: one, which is attached to a light source, and serves to illuminate a sample, and the other which is attached to a spectrometer serves for collecting and transmitting light arriving from the sample.
For their many applications in the fields of chemistry, biology and others and which may include, among others, in vivo measurement of biochemical occurrences in tissues, fiber optic probes must satisfy a variety of requirements such as good optical characteristics, slenderness, flexibility, and sufficient toughness to enable introduction into an endoscope channel.
EP 0358 203 describes a fiber optic probe for measuring a reflectance spectrum. This probe comprises a light illuminating optical fiber and a light receiving optical fiber coupled in parallel to form a fiber bundle which is inserted in a coating tube, and is also provided with a lens placed at the end portion of the fiber bundle which serves as a condensing means. The probe is rather expensive with relatively low efficiency.
Other types of fiber optic probes for IR spectroscopy include an attenuated total reflection (ATR) element for receiving and transmitting attenuated IR light such as in U.S. Pat. No. 5,170,056 and U.S. Pat. No. 5,185,834. Such probes are, however, relatively complex and their manufacture is complicated and expensive.
Research Disclosure No. 295087 of November 1988 describes a device for illuminating fluid samples and collecting scattered and emitted light therefrom. It comprises a fiber-optic probe having at least one illuminating optical fiber and at least one collecting optical fiber, and in order to increase the collection efficiency, the tested sample is contained within a sample tube having a reflective inner surface. The probe and sample tube are separate parts and accordingly in operation they have to be carefully aligned, the accuracy of the measurement being contingent on the accuracy of alignment, which is an obvious disadvantage. A further, fundamental disadvantage of this device is that it is suitable only for sampling liquid materials and is inapplicable for solid ones.
It is the object of the present invention to provide an improved fiber optic probe for IR spectroscopy, free of the above disadvantages and suitable for use on both fluid and solid samples.